In general, the technologies for storing and reproducing the multimedia content data have significantly improved with the industry advances in consumer electronics. In a broad sense, multimedia data can be classified as audio, video, and image content. Typical storage devices for multimedia content include: cassette tape, video tape, compact disc (CD), digital video disc (DVD), memory, hard disk, and portable storage devices. In order to reproduce the multimedia contents the following representative devices are used: cassette tape player, video cassette recorder (VCR), CD player (portable/non-portable), DVD player (portable/non-portable), computer (desktop, laptop, PDA, pocket PC, etc), and MP3 player. The technologies for high-density memory and hard disc have made it possible for portable storage devices to be advanced such that they are able to store the multimedia contents from several hundred Megabytes (M bytes) to several hundred Gigabytes (G bytes)
Currently, most users can obtain multimedia contents by purchasing cassette tape, video tape, CD, or DVD. However, the trend of obtaining the multimedia contents is rapidly shifting due to the advance of wireline and wireless Internet-based technologies and the explosive growth of Internet users. In order to distribute and obtain the multimedia data through the network, the multimedia contents should be stored and distributed in digital formats. Since the conversion of the multimedia contents to digital formats and distribution through the network require a huge memory space and network resources, data compression technologies depending on the contents have been advanced to remove redundant information present in the contents. For instance, MPEG Audio Layer-3 (MP3) is used, in general, to compress audio contents (music, FM broadcast etc) and JPEG is used to compress images. For the compression of video, different methods are used. MPEG-2 or MPEG-4 is used for digital TV broadcasting and AVI (Audio Video Interactive) is used for video on the Windows system.
Since the multimedia contents in cassette tape, video tape, CD, and DVD are selected by the content provider, a user does not have much freedom to choose the contents of his/her preference and much of the contents are wasteful. Furthermore, in order to reproduce the contents, a user should carry a volume of materials that contain the contents. When the portable storage device is used, it has an advantage of portability due to a compact size. However, it has major drawbacks in that a computer should be used when downloading the contents to the storage device and the contents cannot be regenerated through the consumer electronic devices because they do not have-the capability to accept the contents in the storage device.